Trailers are often compartmentalized to provide two or more separate compartments, the air to each being conditioned according to the type of load or cargo to be placed in the compartment. The most common compartmentalized arrangement of a trailer provides two compartments, a front compartment which usually carries a frozen load, and a rear compartment which usually carries a fresh load. A refrigeration unit mounted on the outer front wall of the trailer, called the host refrigeration unit, has an evaporator which serves the front compartment, and the host refrigeration unit also provides refrigerant for a remote refrigeration unit mounted in the rear compartment.
When the front compartment is loaded or unloaded via a suitable front access door, it is common practice to manually shut the host refrigeration unit down. Thus, neither compartment is conditioned while the front compartment is being loaded or unloaded, and the host refrigeration unit must then try to bring both compartments back to the desired set point temperature before the tractor-trailer reaches the next loading or unloading point. If the host unit is allowed to operate, instead of shutting it down, it is wasteful of fuel and it is uncomfortable for the personnel trying to load or unload the front compartment.
When the rear compartment is loaded or unloaded via a rear access door it is common to manually shut the rear refrigeration unit down. If the rear refrigeration unit is not shut down, it wastes fuel.
It would be desirable, and it is an object of the present invention, to be able to automatically operate a compartmentalized trailer for optimum efficiency and enhanced operation, while eliminating any dependency upon timely manual selection of operating modes.